This invention relates to "plungerless" devices for drawing blood and for administering liquids via parenteral injection. In the devices of this invention, the volume of the collection or medication chamber is increased, and negative pressure thereby created, through the action of hinge means connecting rigid plates at least one of which is in continued contact with the exterior sides of the chamber. Different embodiments are described in which the device employs either a separable or integral means for altering the volume of the chamber and thereby causing flow into or out of the chamber.
"Plunger"-type syringes for the collection of arterial or venous blood, or for the parenteral injection of substances, are well known. Tolerances for these plungers are such that it is difficult to achieve consistently a fit that is neither too snug nor too loose. They are too bulky to be inserted at a shallow angle into a blood vessel. They roll easily and are often fragile. Two hands are necessary to create negative pressure within them (one to withdraw the plunger and the other to hold the housing). They do not have components that are reusable without resterilization. Other disadvantages of these syringes are well known to medical practitioners.
Devices which have inherent negative pressure may cause damage to blood cells and to blood vessels, and also have a limited shelf life. They, too, are bulky and difficult to manipulate.
Villari, U.S. Pat. No. 4,187,860 shows a "plungerless" arterial blood collector. It is a passive system designed to exert a minimum of pressure on the collection bag. It cannot be used to draw venous blood and cannot easily be filled completely with arterial blood (i.e., air would not be excluded). In addition, so that his back plate does not interfere with the filling of the bag, his needle adapter must be offset from the back plate. Consequently, the needle of the Villari device cannot be inserted at as small an angle of entry as made possible by the present device.
In the "bellows"-type syringes previously known, Krasno, U.S. Pat. No. 2,717,598, Bane, U.S. Pat. No. 3,340,869, and van Leer, U.S. Pat. No. 3,991,757, measurement of the volume of blood received would be difficult. Neither do they lend themselves to "shallow" injection. There is also a danger of injecting air into the patient.
In the simplest "plungerless" syringes such as Lockhart, U.S. Pat. No. 2,727,516, Gerarde, U.S. Pat. No. 2,907,326, and Pogorski, U.S. Pat. No. 3,662,928 air cannot easily be completely expelled, and one might inadvertently inject air into a patient during phlebotomy.